(1) Field of the Invention
The present invention relates to a quantum computer and, more particularly, to a scalable architecture for a universal quantum computer containing distinct classical and quantum computational units, as well as distinct classical and quantum communication channels.
(2) Description of Related Art
A quantum computer is a computational device that utilizes quantum mechanical phenomena (e.g., superposition and entanglement) to perform operations on data. In a quantum computer, the amount of data is measured in qubits. Conversely, in a classical computer, it is measured in bits. An underlying principle of a quantum computer is that the quantum properties of particles are used to represent and structure data. Quantum mechanisms are then used to perform operations with the data.
A silicon-based quantum computing architecture was proposed by Kane in “A Silicon-Based Nuclear Spin Quantum Computer,” Nature, Vol. 393, pp. 133-137, 1998 and patented in U.S. Pat. No. 6,472,681. Additionally, an ion-trap based quantum computing architecture was patented by DeVoe in U.S. Pat. No. 5,793,091 and also described in DeVoe, “Elliptical Ion Traps and Trap Arrays for Quantum Computation,” Physical Review A, Vol. 58, pp. 910-914, 1998. The Kane quantum computer architecture is further analyzed and extended in Copsey et al., “Toward a Scalable, Silicon-Based Quantum Computing Architecture,” IEEE Journal of Selected Topics in Quantum Electronics, Vol. 9, pp. 1552-1569.
The Kane quantum computer architecture proposal stores quantum information (qubits) in the form of phosphorous atom nuclear spins distributed in a silicon semiconductor. One and two qubit operations may be performed by applying voltages to metallic gates near the phosphorous atoms. Two qubit operations include the swap operation between spatially adjacent qubits, which allows for the communication of quantum information along swap chains or “quantum wires.” Copsey et al. extended the Kane proposal by including long distance communication of quantum information via Einstein-Podolsky-Rosen (EPR) pair distribution and teleportation. Because of the different costs of long and short distance quantum communication, Copsey et al. proposed a hierarchical arrangement for the physical quantum bits storing the logical quantum bits.
There are several major disadvantages to the Kane-Copsey silicon quantum computer architecture. Though Copsey et al. considered the physical limits in placing classical gates near the phosphorous atoms, they did not describe the classical control electronics necessary to perform the quantum operations, nor the spatial structure of the classical control electronics. Additionally, the software to control the classical electronics was not mentioned in respect to the Kane-Copsey architecture. Copsey et al. failed to address the problem of spatial layout of the classical gate control wires and electronics, particularly with respect to the long quantum swap chains necessary for EPR pair distribution. Finally, quantum error-correction in the Kane-Copsey architecture is to be performed entirely within its hardware.
The Devoe quantum computer architecture is based upon arrays of elliptical ion traps. Each ion trap contains multiple ions, with each ion storing a physical qubit. Single qubit operations on ions are performed using properly timed laser pulses. Two qubit and quantum communication operations between ions in a single trap are mediated by collective phonon modes of the trapped ions. Quantum communication between ions in different traps is accomplished by placing the traps in a cavity, and using the photon cavity modes to mediate between the designated spatially separated ions.
Like the Kane architecture, the Devoe architecture does not address the classical control electronics and software necessary to perform the various quantum algorithms. Additionally, the physical location of the ion traps must be such that a cavity photon mode is able to transmit quantum information from one trap to another; distributed ion traps are not supported. However, the Devoe architecture may be extended to use teleportation (Bose et al., “Proposal for Teleportation of an Atomic State via Cavity Decay,” Physical Review Letters, Vol. 83, pp. 5158-5161, 1999; Browne et al., “Robust Creation of Entanglement between Ions in Spatially Separate Cavities,” Physical Review Letters, Vol. 91, 067901, 2003), in which case distributed ion traps are possible. Finally, error-correction is not addressed by the Devoe architecture.
Both the Kane-Copsey and Devoe inventions describe specific implementations of quantum computer architectures. Both of the references fail to provide all the components necessary for a complete architecture for a quantum computer: local quantum computation, distributed quantum computation, classical control electronics, classical control software, and error-correction.
Thus, a continuing need exists for a general quantum computer architecture framework that includes all the necessary components for a complete quantum computer where the components may be implemented using several different technologies.